For example, a fixed type constant velocity universal joint (Rzeppa constant velocity universal joint: BJ) used for the connection between drive shafts or the like in automobiles includes: an outer joint member in which curved track grooves are axially formed on its inner surface with a spherical shape; an inner joint member in which curved track grooves are axially formed on its outer surface with a spherical shape; multiple torque transmission balls respectively arranged in ball tracks formed by cooperation of the track grooves of the inner joint member and the track grooves of the outer joint members corresponding thereto; and a retainer (cage) having pockets for respectively holding those torque transmission balls.
Further, there may be cases where a wheel base is lengthened from the viewpoint of improving the safety of automobile in the event of a crash. In this case, however, in order to prevent a turning radius of the vehicle from increasing, there is a need to increase a steering angle for the front wheels by providing the fixed type constant velocity universal joint with a higher operating angle. For filling the need for such a higher-angle, there is provided an undercut-free type fixed constant velocity universal joint (UJ) in which the track grooves on the opening side of the outer joint member have a straight shape parallel to the axial direction of the joint. In this kind of constant velocity universal joint, there is no under cut formed on either of the outer joint member or the inner joint member so that a higher operating angle can be attained.
Examples of the fixed type constant velocity universal joint in recent years include one having a retainer (cage) increased in strength and durability (Patent Document 1), and one prevented from operational failures liable to occur when a high operating angle is formed and large torque is born (Patent Document 2).
Examples of the fixed type constant velocity universal joint in recent years include one having a retainer (cage) increased in strength and durability (Patent Document 1), and one prevented from operational failures liable to occur when a high operating angle is formed and large torque is born (Patent Document 2).
In the constant velocity universal joint disclosed in Patent Document 1, a dimensional relation between curvature radius of corner radius portions and diameter of torque transmission balls are set in cage pockets. With this setting, surface areas of an inner surface and an outer surface of a retainer (cage) are increased. With this increase and an effect of a decrease in maximum main stress load in pole portions between pockets adjacent to each other in a circumferential direction, the cage can be increased in strength and durability.
Incidentally, in the fixed type constant velocity universal joint of those types, track grooves in the inner race are formed to be deeper at one end portions (inlet side) and shallower at the other end portions (back side) . Therefore, there is a risk that, in the vicinity of the shallower end portion at which the torque transmission balls are positioned when a high operating angle is formed, contact ellipses of the torque transmission balls run onto shoulder portions of the track grooves so as to cause failures such as cracking or swelling of edge portions. Under the circumstance, in the fixed type constant velocity universal joint disclosed in Patent Document 2, a relief portion is provided on an outer spherical surface on a side of the inner race (back side) , on which the track grooves are shallower, while being retracted with respect to the outer spherical surface. With this, even when swelling and the like occur, the relief portion absorbs the swelling and the like so as to prevent operational failures from occurring.
(Patent Document 1) JP 2002-13544 A
(Patent Document 2) JP 11-190354 A